This invention is directed to non-offset image forming devices, such as xerographic or inkjet digital printers and copiers.
Offset printing presses are presses which may print an image lithographically defined on a special plate, by applying ink to the plate and transferring the ink to a sheet of paper via a rubber blanket roller. The output characteristics of the image may be determined, in part, by the amount of ink applied to a given region of the plate. The amount of ink applied may be controlled by an ink key, which may be mechanically or electronically controlled, which controls dispensing of the ink from a reservoir. A plurality of ink keys may be disposed in the cross-process direction of the press, i.e., in the width direction of the sheet, and may be used to determine the quantity of ink dispensed within each stripe region of the image. In general, there may be four ink keys within each region, one for cyan ink (C), one for magenta ink (M), one for yellow ink (Y), and one for black ink (K).
Typically, in offset presses, multiple pages may be printed together on a single sheet of larger size paper stock. The situation is illustrated in FIG. 1, which shows a typical sheet 20 produced by an offset press. Multiple images, eight images 10 in the illustrated case, are printed on a single sheet 20 of paper stock. The printed sheet is output from the press in the direction shown. At various intervals of time, the press operator may remove a printed sheet from the output for inspection.
The operator may determine if areas of the printed sheet need adjustment, for example, if areas of the printed sheet are too light or too dark, or if certain areas of the images, such as flesh tones, need adjustment. To make this determination, the operator may refer to color control bars, consisting of for example, color test patterns 13a and 13b, one of which is printed within each region whose image characteristics may be controlled by a set of four ink keys. The control test patterns may include each of the colors, cyan (C), magenta (M), yellow (Y) and black (K). The operator may determine the density of each of the colors of ink on the control bar, either visually or by using an instrument such as a densitometer. If needed, the operator may adjust the control bars, and thus the printed image, using a set of ink key buttons available on a console 30.
Ink key buttons 50-70 displayed on console 30 may be used to input the operator's selection to a control program, which regulates the appropriate ink keys which regulate, respectively, the flow of ink to the lithographic plate and hence to the printed sheet. The ink key buttons may come in pairs, for example 50 and 52, which increase and decrease, respectively, the amount of each color of ink controlled by the associated ink key from the ink reservoir.
Each pair of ink key buttons, 50 and 52, and 60 and 62, for example, may control the ink dispensed within a certain width 12a and 12b of the printed sheet 20, respectively, as shown in FIG. 1. The widths 12a and 12b may also be the regions which contain the color test patterns 13a and 13b, for example.
While only seven pairs of ink key buttons are shown in FIG. 1 for simplicity of illustration, in reality there may be, and typically are, many more. For example, an offset press may have a set of ink keys for adjusting stripes only about 1.5″ wide.